* than {@code upper}.
   *
   * @throws IllegalArgumentException if {@code lower} is greater than <i>or equal to</i> {@code
   *     upper}
   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
   * @since 14.0
   */
  public static <C extends Comparable<?>> Range<C> open(C lower, C upper) {

    assertEquals("foo", LOWER_CAMEL.to(LOWER_UNDERSCORE, "foo"));
    assertEquals("foo_bar", LOWER_CAMEL.to(LOWER_UNDERSCORE, "fooBar"));
    assertEquals("h_t_t_p", LOWER_CAMEL.to(LOWER_UNDERSCORE, "hTTP"));
  }

  public void testLowerCamelToLowerCamel() {
    assertEquals("foo", LOWER_CAMEL.to(LOWER_CAMEL, "foo"));
    assertEquals("fooBar", LOWER_CAMEL.to(LOWER_CAMEL, "fooBar"));
  }

  public Iterator<E> iterator() {
    return delegate.iterator();
  }

  @Override
  public E last() {
    return delegate.last();
  }

  @Override
  public @Nullable E lower(E e) {
    return delegate.lower(checkValid(e));
  }

  @Override
  public @Nullable E pollFirst() {
    return delegate.pollFirst();
  }

  @Override
  public @Nullable E pollLast() {

    }

    @Override
    public @Nullable E higher(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().higher(e);
    }

    @Override
    public @Nullable E lower(E e) {
      return delegate().lower(e);
    }

    @Override
    public @Nullable E pollFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().pollFirst();
    }

    @Override

    }

    @Override
    public @Nullable E higher(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().higher(e);
    }

    @Override
    public @Nullable E lower(E e) {
      return delegate().lower(e);
    }

    @Override
    public @Nullable E pollFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().pollFirst();
    }

    @Override

  private static final String LOWER = "abcdefghijklmnopqrstuvwxyz";
  private static final String UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  public void testToLowerCase() {
    assertEquals(LOWER, Ascii.toLowerCase(UPPER));
    assertSame(LOWER, Ascii.toLowerCase(LOWER));
    assertEquals(IGNORED, Ascii.toLowerCase(IGNORED));

        NavigableSet<Integer> unfiltered = createUnfiltered(filtered);
        for (int i = 0; i < 10; i++) {
          assertEquals(unfiltered.lower(i), filtered.lower(i));
          assertEquals(unfiltered.floor(i), filtered.floor(i));
          assertEquals(unfiltered.ceiling(i), filtered.ceiling(i));
          assertEquals(unfiltered.higher(i), filtered.higher(i));
        }

    StringBuilder builder = new StringBuilder();
    Writer writer = new AppendableWriter(builder);

    writer.write("Hello".toCharArray());
    writer.write(',');
    writer.write(0xBEEF0020); // only lower 16 bits are important
    writer.write("Wo");
    writer.write("Whirled".toCharArray(), 3, 2);
    writer.write("Mad! Mad, I say", 2, 2);

    assertEquals("Hello, World!", builder.toString());
  }

    return RANDOM_SOURCE.nextBoolean() ? result : result.negate();
  }

  /**
   * Chooses a number in (-2^numBits, 2^numBits) at random, with density concentrated in numbers of
   * lower magnitude.
   */
  static BigInteger randomBigInteger(int numBits) {
    while (true) {
      if (RANDOM_SOURCE.nextBoolean()) {
        return randomNonNegativeBigInteger(numBits);
      }

    assertEquals("foo", LOWER_CAMEL.to(LOWER_UNDERSCORE, "foo"));
    assertEquals("foo_bar", LOWER_CAMEL.to(LOWER_UNDERSCORE, "fooBar"));
    assertEquals("h_t_t_p", LOWER_CAMEL.to(LOWER_UNDERSCORE, "hTTP"));
  }

  public void testLowerCamelToLowerCamel() {
    assertEquals("foo", LOWER_CAMEL.to(LOWER_CAMEL, "foo"));
    assertEquals("fooBar", LOWER_CAMEL.to(LOWER_CAMEL, "fooBar"));
  }